JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2017-0022 Natural Sci 2017, Vol. 61, No. 3, pp. 181-190
This paper is available online at hnp://stdb.hnue.edu.vn
XAC DJNH PHAN B 6 L U N DAT T^I THANH PHO HA NOI BANG PHUONG PHAP GIAO THOA RADAR
D a n g V u K h a c
Khoa Dia li. Trudng Dgi hgc Suphgm Hd Ndi
Tom tat. Bang phuang phap giao thoa radar da thdi gian, chung toi da khao sat phan b l cua hien tirgng lun dat tai thanh pho Ha Npi tfl anh ALOS PALSAR trong giai doan tu thing 2/2007 den thing 2/2011. Ban do thu dugc cho thay bd Bac cua sdng Hdng co ve dn djnh, trong khi do bd Nam dang bj lun vdi van tdc tmng binh cyc dai tdi 68 mm/nam. Biln d?ng xay ra tai 3 qu|in npi thanh ia Hoang Mai, Ha Dong, Tfl Licm, noi tap tnang nhilu cong trinh xay dyng va cac tram hut nudc ngam trong thap ki vfla qua. Ngoai ra, mpt so khu vyc vdi quy mo nho han trong khu vyc ndi thanh ciing b] lun dai de dpa. Cac kit qua nay tucmg dong voi cic gia tri do bing phuong phip thuy chuan do Tdng cong ti Diu lu Phat triin nha va Do thj tien hanh trong giai doan tu thing 2/2007 din thing 6/2008. Dilu nay chung minh kha nang ap dung phuang phap giao thoa radar vao theo doi lun dat vdi dp tin c?iy cao va gia thanh hpp li de bo xung thong tin cho cac phuang phap do mat dat.
Tu-khoa. Lun dat, giao thoa radar da thdi gian, vat tan xa codjnh, thuy chuan
1. Mo'dau
Hien tugng lun dat do khai thac tai nguyen thien nhien dudi long dat ngiy cang phd bien trong nhflng thap nien vfla qua do nhu cau tieu thy tai nguyen ngiy cang tang cfla xi hdi loai ngudi [1]. Lun mat dat dang dugc die biet quan tim khi nd xiy ra tai nhieu thanh phd, nai ma qua trinh do thi hda mgnh me keo theo sy gia tang nhu cau tieu thy nude vdi lugng nudc ngim Idn duge hflt len tfl Idng dat. Van de niy da dupc ghi nhan tai cae thanh phd ldn nhu: Mexico-City, Bangkok, Thugng Hii, Venice, va Las Vegas. Tfl nhflng nam 1960, cic nghien euu ve liin dat da dugc thyc hien vdi nMlu phuang phap khio sat [2] de cd nhflng Meu biet lot han ve ca che hinh thanh [3] va ve hau qua tie ddng len mdi trudng [4]. Cac ki thuat do dae biln dang bl m^t mpt each djnh lugng thay ddi lu phep do mat dit nhu phugng phap thfly chuin [5] va phuang phap do gian kl [2] tdi ki thuit khdng gian nhu phuang phap do GPS ttnh [6], phuang phap giao thoa radar InSAR [7], hay phuang phap LiDAR hang khdng [8].
Thanh phd Ha Ndi la mgt vi dy diln Mnh ve thirdi phd cd tde do do thi hda nhanh trong cac nudc dang phit trien, nai ma nudc ngam li ngudn tai nguyen chinh cho nhu cau nudc sach [9].
Hien tai, thanh phd nay dugc chia ra thanh 10 quan npi ihanh, 19 huyen ngoai thinh sau bdn lin dilu chinh dia gidi hinh cMnh. Dieu nay cho phep chuyin ddi dat ndng nghiep ngoai d thanh dat do Ihi vdi viec thanh lap mdt sd quin mdi nhu Tay Ho nam 1995, Thanh Xuan va Cau Giiy nam 1996,
Ngay nhan bai: 6/1/2017. Ngay nhan dang: 20/3/2017.
Tac gia lien h?: Dang Vu Khac, email: dangvukhac@gn-
Dang Vu Khac
Long Bien vi Hoing Mai nam 2003 vi Hi Ddng nam 2008 (HiMi 1). Do dd, din so loan thanh pho tang tfl 2,431.10* tdi 3.184.10* ngudi tfl nam 1995 den nam 2006, trong khi dan sd cua cac quin ndi thanh tang gap ddi tfl 1,082 10* len 2.050.10* trong cflng thdi ki Sy gia tang dan sd dat den 6.472.10* vao nam 2009 vdi mil dp la 1979 ngudi/km' va xap xi 35000 ngudi/km' tai mdt so quin Irung tam nhu Ddng Da hay Hoan Kiem [10].
Su tap irung dan cu va phat trien kinh te xa hdi nhung nam qua lam cho nudc ngam hi khai thac manh me tfl mpt sd bii gieng hul nudc ngam a cic quan mdi thinh lap vdi su hinh diinh cfla ba nha may nudc mdi dugc xay dyng trong giai doan 2002 - 2005, ma cong suat efla mdi nha may cd the dat klioing 30000 m'/ngiy dem [11], Hien txtang ha thap myc nudc ngam [12] cung vdi viec phit trien nlii cua tren nen dit yeu da dan den lun dat cue bd va gay ra nhieu hu hdng cho cdng trinh ha tang, nha a cua eu dan va ke ca mdl sd tda nhi cao ling cu. Trong bdi canh qua trinh dd thi hda dien ra Mianh chdng sau kM sit nhip tinh Hi Tiy vao thanh phd Ha Ndi nam 2008, su Meu biel tdt han ve bien dang mat dit tai thanli phd mdi - dugc xic dinh bdi Dd dn Quy hoach chungXdy dirng Thu do Hd Not den nam 2030 vd Tdm nhin den ndm 2050 trd nen cap bach vl day se li nai tip trung phit trien nhieu cong trinh xiy dung quan Irpng trong tuang lai. Muc deu la mpt mat nhim trien khai quy hoach cM tiet mdt each hpp li va mil khac la de khuyen khich cic giii phap kT thuit xay dung cong trinh an loan d nhiing nai bi lun dat de dpa.
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Hlnh 1. Bdn do thdnh phd Hd Npi, v&i vi tri ctia cdc quan npi tlianh vd huyen ngogi thanh {13}
Nhflng nghien cflu trudc diy dya tren phuang phap do dac m§l dit [14-16] hay md hinh hoa MiQng dac tinh Id thuat eua dat [17] da clii ra mgi sd nai thude cae qu^n ndi ihanh bj tic dpng cua bien dstng be m|l trong vai thip nien vfla qua. Chang han nhu. khao sat mat dit cho ihay nd bj jun manh han g khu vuc ngi tlianh han la khu vuc ngoai vi, die biet gan eic gilng hut nudc ngim.
Mflc dp lun trung binh thay ddi tfl 1.4 mm din 41 min'nam trong giai doan 1994 - 2005 [15].
Xdc dinh phdn hd lun ddt tai thdnh pho Hd Npi bdng phuong phdp giao thoa radar Tuy nhien, cac phuang phip do dac mat dat nay klidng iMch hgp de tlieo ddi bien dgng tren dien rpng nhu Ifln dit vi chflng chi cung cip thdng tin tai mdl vai diem khio sat don le. Trii lai, cic tinli loan dya iren phuong phap giao thoa radar - InSAR cung cap thdng tin ve hien trang lun dat Iren khu vyc rgng Idn vdi dp chinh xic bien ddi tfl vai cm den vii mm tfly thudc vao ki thuit su 'dimg. Vdi phuang phip niy, mdl so nghien cfluda tip trung vao bien dang mat dat tai trung tim npl thanh [18-23] Vdi ki thuit InSAR iruyen thdng, cic nghien eflu da ehi ra su dich chuyen theo phuang thing dflng vdi gia trj 20 mm trong giai doan 1996 - 1998 lai day [18].
Tuy nhien, cac tac gia khdng thu dupc tdc dp lun cfla ci thanli phd Ha Ndi (Hinh 1). Hon nfla each Hep can cfla hp chiu mpt sd han che ea bin efla kl thuit giao thoa. Thfl nhit, sd lugng anh cd han cfla inh radar kenh C (chfl yeu li ERS vi Envisat cfla ca quan hang khdng vu try Chiu Au- ESA) [19] vi sy khdng phu hgp khi Id hgp giua cac anh radar do dudng ca sd thdi gian va khdng gian phan each nhau kem hgp It. Hon nfla, thdt tiet Mflet ddt sinh ra cac nMeu kM quyen dang ke trong dfl lieu iMi radar [24], die biet d ling doi lun cho cac anh thu tren kenh C (budc sdng 5.6 cm) [25], Han che nfla cd the lien quan tdi su mat tirong quan gay ra do nhflng bien ddi ve dac tinh tin xa cfla mat dit, chu yeu la thyc vit trong khu vue nghien cfln [26]. De vugt qua eac khd khan nay, chflng tdi xfl Ii 22 anh thu tren kenh L efla ve tinh ALOS PALSAR (budc song 23.62 cm) bing phu-ong phap giao thoa trong giat doan 2/2007-2/2011 vdi muc lieu dat ra nhu sau: 1/
Ve ban dd phan bd khdng gian cfla Men lugng lun dat trong giai doan 2/2007-2/2011, 2/ Xae dinh van tdc lun trung binh theo chieu thing dung cho loan bd thanh phd.
2. Noi dung nghien cmi 2.1. Phu'OTig phap luan va so lieu sii' dung 2.1.1. Phinmgphap giao thoa radar
Viec su dung kT thuit giao thoa radar (InSAR) de do ve be mat Trii Dat, gdm ci viec thinh lap be mil dia hinh va xac djnh biln dang mat dit, da dugc minh chflng mdt each thinh edng tfl han hai thip ki qua [27]. Phucmg phap giao thoa truyin thdng cho phep tao ra cac anh giao thoa nrang flng vdi sy lech pha khi chup inh lap lai nhieu lin. Sy lech pha efla cic pixel dan le niy tu-ang ling vdt mot sd thanh phin;
$ = Z(A(Pu,i,+A{p,opo+Aq)u,m+AlpK+A9def) ( ' )
6 day, Acporb, Aipiupo, Aipji^,, va A(pd=r la sy lech pha lin lugt gay ra do vi tri cfla quy dao, dia Mnh, tre kM quyen va biln dang bl mat. Thanh phan nhilu AipN lien quan ldi muc dp bten ddi cfla tan xa, nhieu nhiet va sai so trong xfl li sd lieu. De thu duac thanh phin bien dang vdi dp chinh xac cao, viec udc tinh ldi cac thinh phin khac la can iMlt, dya tren sd lieu eWnh xac ve eic tham so quy dao va dia hinh. Thanh phin biln dang cd thi dugc bilu dien theo cdng thuc:
Atpdei ^ 47t(ARyX) (2) Vdi AR la sy biln ddi vl khoang cich gifla v? tinh va m^t dit dgc theo hudng quan sat efla ve
linh va X li budc sdng cua he thdng radar.
Do rit Miay cam ddi vdi djch chuyen thing dflng, viec llieo doi hien tugng Ifln bang phuang
phap giao thoa radar da trd thanh mdl Uong nhflng flng dyng chi'nh [28], dac biel irong khu vuc dd
thi nai ma sd lugng pixel dn dinii theo thai gian khi phong phfl [29]. Phuang phip InSAR cflng
da du-gc su dyng trong nghien cfln hien tugng Ifln tai khu vye dd thi va cac tie gii cho thay be mat
dia Mnh mdt sd thinh pho nhu tai thinh phd Ho Chi Minh bi lun ding bio ddng vi ki thuat giao
thoa vi phan la rapt giai phip kha thi nhat irong viec phat hien eac bien dang be mil dia Mnh iheo
klidng gian va thdi gian [30] Tuy nhien, sy mit tuong quan gay ra hoic do su thay ddi cfla hudng
quan sat ve tinh ddi vdi hai inh (cic gdc nMn khac nhau), hay sy thay ddi ve vj tri efla val lin xa,
183
Dang Vu Khac
hay sy thay ddi ve Mnh hpc ben ttong d ca sd. Neu su mit tuang quan ldn, inh giao thoa se khdng tMch hgp cho viee phan tieh bien dang. Trong trudng hgp sy bien dang xiy ra manh, thinh phan Aqjdcf chiem uu the thi nd cho phep xie dinh dugc dich chuyen gifla hai lin thu anh [31]. Tuy nhien, trong trudng hgp vdi djch chuyen chim, vide xac dinh thinh phin bien dang cd the bi gidi han bdi sy not trdi cfla cic thinh phan khdng bien dang trong phuang trinh (1). Bang each phan tieh nMeu inh giao Ihoa cfla cflng mot khu vyc lai nhieu thai diem khac nhau, ti sd tin hieu/nhilu dugc ning len, cho phep xac dinh van tdc dich chuyen trung binh cfla mat dat trong giai doan bao trflm bdi cac inh giao thoa [32].
D I vugt qua su mat tu-ong quan ve thdi gian do su Ihay ddi ve die tinh tin xa, giim tie dong cua khi quyin va do cic dich chuyen lam thdi; ki thuat giao thoa da thai gian mdi duge phit trien.
Ki thuat nay dya iren viee thu nhan ahiext inh radar dng mo tdng hgp vi bao gdm each liep can Persistent Scalterers (PS) va Small Baseline (SB). NMn chung, hai each liep can nay rat ldi uu de xfl Ii nhihig vat tin xa tren mil dat. Phuang phap PS nham vao cac d ca sd ndi trdi bdi mgt vat lan xa dan le, trong khi phuang phap SB hirdng tdi xfl li cic 6 ca sd khdng cd val tan xa ndi trdi.
Trong ngMen cfln nay, chflng tdi sfl dyng phuang phap giao Ihoa da thdi gian StaMPS/MTI dupe phat trien bdi Hooper. Phuang phap nay to hgp ei hai cich tiep can PS vi SB de lach ra dau hieu biln dang l?i cac diem arfli vi lim tang ti sd lin hieu/nMeu. Vice lua chpn diem anh PS dugc thue Men diu lien bing each sfl dyng cich tiep can PS dugc phat trien bdi [33], va sau dd mpi loat anh giao thoa thu hai dugc xfl li bang cich tiep can SB de xae djnh cic vat lin xa ddng deu (DS) ma ddi vdi chdng tM gia tri pha khdng bi mat tuong quan dang ke trong mpt khoing thdi gian ngin.
Viec sfl dung phuang phap giao thoa da thdi gian, diu Meu bien dang duge tach ra tfl ca cae diem inh PS vi DS, cho phep lam tang sd lugng mau quan trie vi lam qua trinh md pha dien ra tdt hon.
Dau lien qua trinh md pha 3-D sfl dung phuang phap thdng ke gia [34], vi viee udc lupng sai sd cua md hinh sd dp cao bang mdi tuang quan vdi cic gii tri cfla dudng co sd vudng gdc ciia iflng anh giao thoa de md pha lan thfl hai cd linh den cac sfla ddi nay. Cho tdi thdi diem hien nay, mpt sd ung dung cfla phuang phap nay da tap trung nghien cflu Ifln dat trong dd thi nhu nghien cflu cfla [35].
2.1.2. So lieu
Chflng ldi sfl dung 22 inh radar dugc Ihu chyp Iren kenh L (budc sdng 23.6 cm) trong thdi gian tfl thing 2/2007 den thing 2/2011 bdi diu thu PALSAR dat tren ve tinh ALOS cua Nhai Bin.
De giam tMeu sy mat luang quan ve thdt gian vi khdng gian, inh tham chieu dugc chpn luang ung vdi anh tham chilu chup ngiy 25 thing 6 nam 2009 cung viec sfl dyng ngudng 2000 m flng vdt dudng CO sd khdng gian va 4 nim ung vdi dudng co sd thdi gian 20 inh giao thoa dd duac ttnh toin so vdi anh tham chieu trong phu-ong phap PS vi 46 anh giao thoa dd dugc tinh iheo phuang phap SB. Do kich thudc 1 cinh inh ALOS kha rpng (70 x 70 km), nen nd bao trflm len 1 khu vyc vdi nhieu dahg dia Mnh vi sy bien thien manh mS cua dac diem vi khi hiu. CMnh vi vay de giam di su chenh leeh cfla cac ylu Id gay nMeu eho qui trinh phan lich giao thoa, chung toi lien hanh chia khu vue ngMen cuu ra thanh 4 phan vdi kich thudc 35 ^ 35 km (Hinh 1). Sau khi xfl li, ban dd ket qui cho ci thanh phd dugc gdp lai tu 4 manh dan le. De loai bd thanh phan dja Mnh trong anh giao thoa, chung tdi dung md Mnh sd dp cao loan cau SRTM V.4 vdi dp phan giii 3". M^t khac, thanh phan quj dao dugc loai bd bang each sfl dung sd lieu quy dgo vdi dp chinh xae < I m do JAXA cung cap trong dau dan cfla t?p tin di cflng vdi inh radar.
2.2. Ket qua nghi&n cuu
2.2.1. Phin bo khong gian va van toe cua hien tugoig lun
Sfl dung phuang phap phan lich chudi sd lieu da Ihdi gian mdl sd lupng ldn cic vat tan xg c6
djnh (540000 diem SP) da dugc chgn lya irong khu vuc nghien cuu (Hinh 2).
Xdc d\nh phdn ho lun ddt tgi thdnh pho Hd Npi bdng phirong phdp giao ihoa radar
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ffin/i 2. t'pn tdc lun trung hinh theo phuang thdng duTig tgi thdnh pho Hd Npi thu dug'c tuxiriiInSAR cho giai dogn 02/2007-02/201L Khung tim Id vi tri cua Hinh 3c, 3b vd 3c
Phan ldn cac val tan xa nay tuang ung vdi nhi a, nhi cao ting va cdng trinli ca sd ha tang, nam trong khu dan cu ddng due efla cac quin ngi thinh. Cdn d cic huyen ngoai thanh, chung tucmg flng vdi eac lang xdm tren ddng bing hay cic dipn Id da gdc yen ddi nfli. Nhflng vj tri khdng cd vat tan xa dn dinh tuang flng vdi mat nudc hay cac rupng ddng ndng ngMep xung quanh khu vuc dd thj. De dam bao hau het cac bien dang do dugc luang flng vdi sy dich chuyen cfla mil dit do lun theo phuong thing dung, chung tdi chuyen ddi van tde lun ihu dugc theo hudng ngim cua ve tuih thanh van ldc Ifln theo phuong thing dung vdi gdc tdi (8) tai tflng diem anh (6 trung binh = 38°
ddi vdi inh ALOS) Iheo [36].
Chung tdi quan sat thay sy khdng ddng nhat ve van loc lun trong vung dd iM cfla thanh phd
Ha Npi, vdi van ldc Ifln bien ddi ifl 0 din 68 mm/nam irong khoang thai gian bdn nam nghien cflu
(Hinh 2). Diu lien, chung tdi nhan thay su bien dang bi gidi hgn chu yeu trong vung dd Ihj. Van
toe lun trung binh chi ra su khac biet rd ring giira phin phia bac va phan phia nam cua sdng
Hdng. CJ bd pMa bic sdng Hong, mat dat cd ve nhu li rat dn dinh. vdi mdl vii diem lun nhd ed the
nhin thay d phia ddng huyen Ddng Anh va khu vuc gifla sdng Hdng va sdng Dudng, nhu tgi khu
vyc trung lam quin Long Bien hay phan pMa tay nam huyen Gia Lim (Hinh 2). Ddi vdi cac diem
eye bd nay, kich thudc theo cMeu ngang cfla chflng khdng qui 1-2 km^ mdi diem, van tde lun
trung binh theo phuong thing dung tdi da li 15 mm/nam. CJ bd phia nam sdng Hdng, nai giip
sdng, tuang flng vdi cic qugn Tiy Hd, Ba DiMi, Ciu Giay va huypn Tfl Liem cd the phan biet rii
ro vdi cac bien dang nhd, ngoai tru khu vyc dpe song Hong, noi ma lun dat xay ra vdi tde dp
cham, nhd han 10 mm/nam.
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(a) _ (b) _ (c) Hlnh 3. Bdn do phong to vd ldt cdt cua toe do lun ciia cdc diem tdn xa co dinh thu du^c lirxu li dnh radar lai (a) khu vuc lun Hodng Mai (h) khu vifc lun Hd Bong -Thanh Xudn (Khung mdu tim trinh hdy khu vfft- iheo doi hin hang phirong phdp do mdl ddt lgi khu do thi ni&i Vdn Qudn). vd (c) khu vuc lun Hodi Due - Tir Liem Vi iri khung hinh vd ihang mdu, tham khdo Hinh 2)
Cl phia nam sdng Hdng, lun dai xay ra trong 3 khu vuc chinh ve phia nam va phia lay cfla cac quan trung lam (Hinli 2). Dau lien, khu vyc ldn nhil tuong ung vdi qugn Hoing Mai d phia nam cfla trung tam thinh phd Bien dang tuong flng vdi van ldc Ifln trung binh Idn han 30 mm/nam va bao triim dien tich 5 x 5 km, va dugc bao quanh d phia bac bdi nhung bien thien van tde lun rat dot ngpt (Hinh 2 v i Hinh 3a) Vgn tdc lun trung binh tdi da dat 68 mtn/nim, cM each khu vye on djnli 1 km. Chung tdi ghi nhin hai vung bien dgng rpng vdi kich thudc 2 ^ 2 km trong khu vyc Ifln chinh va mdl sd diem lun vdi kich thude khdng qua 0,5 x 0,5 k m v a tdc dp lun dat 50 miii/nim d phia ddng cua kliu vue lun thfl nhat nay, Khu vyc lun thfl hai nam tgi quan Ha D d n g - Thanh Xuan d phi'a lay nam cua trung t i m thanh phd (Hlnh 2 v i 3b). Ki'ch thudc ngang cua khu vuc liin nay rat ldn, tdi 7 x 4 kin nhung il vi tri trong khu vuc nay the hien ldc do Ifln t h i n g dflng vugt qui 45 mm/nam. Chung tdi chi nhin ra mpt nidi vl tri nhd vdi tdc dp Ifln 60 mm/nam a pMa nam. 0 phia lay cua viing do Ihj. khu vue lun ehinh thu ba ed ve hien ra mdt each md nliat do sy phin tan cua cac val tin xa d huyen ngoai thanh Tu Liem - Hoii Due, nai ma nhung cinh ddng ndng nghiep van cdn chiem uu the (Hinh 2 v i 3e). Cac diem lun vach ra mdl khu vyc 8x3 km' keo dm theo hudng nam bac ma d do van ldc thing dung thay ddi tfl 30 den 60 mirv'nam Trong nhieu phan k h i c cua vung do thj, mpt sd diem lun vdi kich thudc nhd han I km" phan bd lai cic quan npi thanh nhu Ddng Da, Thanh Xuan, hay Hai B i Trung vdi van tdc theo chieu thang dung thay ddi tfl 10 den 25 mm/nam, nghia la nhd han nhieu so vdi ba khu vyc lun cMnh da md ta.
2.2.2. Kiem chu-ng ket q u a
De kiem chflng ket qua xfl li InSAR cua minh. chung tdi so sanh ldc dd lun Iheo phuoi^
t h i n g dflng cho mdt khu vuc cu the, nai cd s i n sd lieu d o dac b i n g phuang phap thfly chuan. Tu n g i y 25/6/2007 din ngiy 26/9/2008, Tdng cdng ty D i u tu' Phai triin Nha va Do thj lien hanli mudi sau dgi do mat dit tai mdt sd khoi n h i irong khu dd thj mdi Vin Quan nam d khu vyc Mn thu hai Ha Ddng - Thanh Xuin (vj tri tren Hinh 3b).
Xdc dinh phdn bo lun ddi tai thdnh pho Ha Npi bdng phuong phdp giao thoa ladar
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Hinh 4 (a) Khu vuc dirae theo doi liin bdng phuong phdp do mat ddi lai khu do ihi in&t Vdn Qudn Vt Iri ciia khu vifc do mgi ddt. iham khdo Hinh 3h. vd cdc diem anh trong khu vuc (ihang mdu). iham khao Hinh 2. (b) Bieu dd do lun lich lHy cua khoi nhd TTI8A. Ngudn (MJ (c) Biiu do ciia mpt vgt idn xa c6 dinh ndm tren khoi nhd TTIHB vd gid tri do lun ciia na bdng phuong phdp do ihiiy chudn Diem thd 3 cua phdn dch InSAR theo chudi thdi gfan ndm doc theo duong hdi quy ciia .so heu do hdng phuong phdp thuy chuan
Chflng ldi xem xet mdt each cu the hon sd lieu do mat d i t cua cac khdi n h i TT18A va TT18B do su tdn tgi cfla cic diem tan xa ed dinh tren cac khdi n h i nay (Hinh 4a) Van tdc lun trang binh suy ra t u sd lieu do mat d i t tuong ung vdi van ldc trung binh 35 mm/nam doi vdi khdi nha TT18A va 27,8 mm/nam ddi vdi khdi n h i TTIXB (Hinh 4b). Dieu nay thuyet phuc rang cac gii in trung binh do phfl h c ^ vdi kel qua xu li InSAR eua chung tdi vdi gii tri 38,2 mm/nam va 25,6 mm/nam doi vdi cac diem tin xa cd dinh nam tren cac tda n h i tuang flng. Tuy nhien, chung toi thay rang cac gia trj n i y nhd han vgn tdc trung blnh 90 mm trong thdi gian 17 thing (tfl ngay 2/2/2007 den ngay 22/6/2008) luang flng vdi 63,5 mm/nam cho loan bp vflng ngliien cfln da dugc [20]
xac diMi. Giai doan sau t h i n g 6/2008, do klidng cd du lieu d o Ihiiy chuan nen chua the kiem chflng du-gc ket q u i xfl li giao ihoa. Tuy nhien ehiing la nhgn thay xu the chung la cac gia trj van tdc tinh toin giam di the hien mat dat bi lun xudng.
Nhu da d l cgp tdi d ben tren, nghien cflu cua Vdge chi xfl li hai anh b i n g phuang phap DInSAR, vdi tat c i c i c bat djnh cd lien quan do su khdng ddng Miit ve khi quyen, su mat tuang quan do thdi gian, v.v... Chung tdt nhan thay s y tuang ddng ldn gifla sd lieu InSAR va so Heu do mgi dat trong giai dogn 6/2007 den 9/2008, dieu nay mang linh quylt djnh doi vdi viec danh gia kel qua thu d u a c t u phuong phap giao thoa radar InSAR (Hinh 4c). Trong cung giai doan c i hai tap hgp sd lieu khdng niin theo h i m sd tuyen tinh, phu hgp vdi van ldc khdng ddi, nhung vach ra mpt ham sd da thflc bac hai. Dieu nay cho thiy sy suy giam chgm cua van toe lun theo phuang thing dflng theo thai gian, no bieu Id ddng thai cua ldp dat chiu sy giam ap lye Id rong do hul nudc ngam. D o dd. trfl cac nliieu ldn chfla trong sd lieu ddi vdi giai doan sau 9/2008, Ifli hieu lun l i rd rang khdng dn dmh nhung bao gdm nhflng dich chuyen tam thdi.
D5ng Vu Khac
N g o i i ra, trong giai dogn 2012 - 2013, chung tdi da tiln h i n h cic hanh trinh thyc d j a d e doi sanh c i c khu vyc bi Ifln xac dinh dupc bang phuang phap giao thoa da Ihdi gian vdi thue te ngoai Men trudng. Tai mdl sd khu dd thi mdi nhu: Ddng T i u , Dgi K i n t D i n L u (quan H o i n g Mat), Van Phfl (quan Ha Ddng), Kim Chung, Di Trach (huyen Hoii Due) chflng tdi ghi nhin cic thiet hai do Ifln d i t gay ra
Hinh 5. Khu do thi mdi Ddng Tau, qugn Hodng Mai (khu vuc lun mgnh nhat)
3. Ket luan
Sfl dung kl thuat giao thoa radar, ehung tdi k h i o sit bien dgng mat d i t lien quan tdi lun dat, Phuang phap n i y to ra cgnh tranh vdt c i c kl thuit do mat dat truyen thdng lien quan den thdi gian va g i i thanh nhd thuat loan ngay cang dugc cai thien va sd lieu ve tinh radar ngay cang phong phfl. Cach liep can phan tich chudi sd lieu da thdi gian cung cap mot dp phfl khong gian hoan cMnh ve khu vyc nghien cfln va viec su dung cic i n h v e tinh ALOS thu chyp tren kenh L cho phep chung loi vugt qua v i n d e mat tuang quan trong vung nMet ddi nhu thinh phd Ha Ndi. Nhd dd, bin do van tdc syl Ifln trung blnh cfla thinh phd Ha Ndi dupe x i y dyng. B i n do nay chi ra toe dd Ifln theo phuang t h i n g dflng trung binh bien ddi lu 0 den 68 mm/nam, va cic vflng bien dgng ldn nhai tuang ung vdi ba khu vyc d qugn H o i n g Mai, quin Ha Ddng - Thanh Xuin v i huy§n Hoii D u e - Tfl Liem. Nghien cun n i y chi ra r i n g phuang p h i p p h i n tich chudi sd lieu radar da thdi gian cd hieu q u i ddi vdi nhung khu vyc nai cac cdng trinh nhan tao chiem uu the nhu mdi trudng do thi. Nhung ddt vdi c i c canh dong ndng nghiep, viec x i c djnh lun se khd khin han do thieu cae vat tin xg cd djnh. Trong trudng hpp nay. can tMet phii phdi hgp mdt sd phuang phap giao thoa radar de cd ket q u i phan tich bien dang ldt han.
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Identification of the land subsidence at Hanoi by interferometry radar D a n g Vu Khac Faculty of Geograffhy. Hanoi National University of Education With a multi-temporal InSAR approach, we investigate land subsidence m Hanoi city from ALOS PALSAR images over the 2/2007 - 2/2011 periods. The map of mean subsidence rate reveals that northern bank o f l h e Red river appears stable, whereas some areas tn southern bank are subsiding with a mean vertical rate up to 68 mm/yr. The deformation occurs within three urban districts of Hoang Mai, Ha Dong and Tu Liem, where construction development and groundwater pumping have been very effective during the last decade. In addition, we mention about several sectors subsided with small extension witlfln urban districts. The results obtaMed by interferomelry radar are similar with the values measured by leveling method over the 2/2007 - 6/2008 periods. This fact proves an applicability of interferometry radar into land subsidence monitoring with high reliability and appropriate price.
Keywords: Land subsidence, multi-temporal interferomeyy radar, persistent scatterers, levelling.
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